well, I was thinking of making a pot-module, like a volume pot in a box that you put before the amp. saves space when portable cause I wont need the pot (and my tin isn't big enough for one), but enables you to use the amp without adustable outputs.

thing is, the cheap 10kOhms pot I got mistracks between 0.40 kOhms and 0.80 kOhms. how bad is this?

if it's not too bad, I'm going to use it with the lower resistance on the right channel as my right ear is not as good as my left one (volleyball seems to be the thing that does it, smashing sometimes makes my ear ring. I'll play volleyball till I'm loosing limbs tho).

so, whaddya think? is it like "whoa thats bad!" or more like "should be okay"?

Wait, just re-read that. You mean mismatched between channels at a specific point? Same thing applies, the lower it is, the more sensitive it's gonna seem. It's rare for a multigang pot to track perfectly. I don't think it's possible. A stepped attenuator or a digital potentiometer is the only way...

If you wanna know at a specific point you'd take a voltage divider and figure it:
dBV = 20*log(Vin*(Rlo/(Rhi+Rlo))

Then you can see how much it'll matter at a specific point in the rotation.

This is just the input attenuation! You have to multiply in the gain because ultimately this is what makes it to your ears; the amp's output.